Method and apparatus for optically measuring the topography of nearly planar periodic structures

ABSTRACT

The present invention discloses a non-destructive method and apparatus for measuring the 3D topography of a sample having periodic microstructure deposited onto the surface, or deposited onto a film, or buried into the film or sample. In particular, the present invention relates to an optical system and method utilizing polarized light beam, diffracted from the repeated structure, to measure its spatial geometry giving parameters such as profile height, profile widths, sidewall angles, and arbitrary profile shape. The optical system employs a broadband or semi-monochromatic light source to produce a light beam that is polarized and focused onto the periodic structure being measured. The focused beam consists of a whole range of illumination angles that is provided to the structure simultaneously. Transmitted or reflected diffracted light generated by the interaction of the light with the periodic structure is collected by an imaging detector system. The detector records the diffraction light irradiance resolved into illumination angles, diffraction orders and wavelength. The data is applied to determine the geometrical profile of the periodic structure using a reconstruction algorithm that is based on comparisons between measured diffraction data and modeled diffraction irradiance of a profile model using Maxwell&#39;s equations. The reconstruction of the profile is performed by iterative adjustments of a profile seed model until the modeled diffraction irradiance matches the measured data within a predefined convergence tolerance.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for opticallymeasuring the topography of locally periodic microstructures on a nearlyplanar surface or embedded into nearly planar stratified structures. Inparticular, the present invention relates to an optical device utilizinglight diffracted from semi-periodic microstructure to determine thetopography of the structure.

BACKGROUND OF THE INVENTION

Process and quality control of semi-periodic microstructures withstructures ranging from microns to nanometers plays an important role infabrication of optoelectronics, optical and microelectronic devices. Oneapproach to perform quality control on a microstructure is to detect thediffracted light intensities from the microstructure. The lightintensities for the different diffracted orders together with a computeralgorithm may then be used to produce a topographic image of themicrostructure.

Process and quality control of microstructures includes illuminating themicrostructure with broad banded light, and measuring the diffractedintensities for all wavelengths and diffracted orders. These data arethen used to generate a topography image of the microstructure using acomputer algorithm. The illuminating optics is positioned in thevicinity of the microstructure surface and perpendicular to it foroptimal detection of the diffracted intensities. The diffracted lightorders are collected by collimating optics and incident on a detectorsystem. The detector system may collect those orders parallel or one ata time.

For each wavelength the intensity of the diffracted orders form adistributional pattern, which may be used to uniquely determine themicrostructure topography using a computer algorithm. The measurement israpid and non-destructive since the invention is based on an opticaltechnique.

There are a number of existing techniques available for measuring thesurface topography of samples having such small structures. Theseinclude:

Electron beam imaging is a technique where a focused electron beam isprovided to create an image of a specimen. For microstructure studiesthe prevalent method of using a focused electron beam is the scanningelectron microscopy (SEM). The electron beam creates secondary electronsoriginating from the upper part of the surface and the generation ofthese electrons depends on material and geometry. Thus an image isobtained by measuring the current of secondary electrons from scans ofthe beam across the surface. SEM is capable of measuring features of 1nm.

However, electron beam imaging has some drawbacks:

-   1. The method does not reveal depth information-   2. Destructive method when profile of the structure is measured by    cross-sectional technique-   3. Sample environment during measurement is vacuum-   4. Conductive coating of non-conductive structures is necessary in    order to enhance the generation of secondary electrons. This alters    the structure to be measured.-   5. Build-up of surface charge affects the measurement resulting in    distorted images

Scanning probe microscopy (SPM) utilizes a small mechanical probebrought very close to the surface of the specimen detecting theproximity of surface atoms. By this technique an image of the surfacetopography is obtained by scanning the probe across the surfacerecording the vertical (height) adjustments of the probe such that aconstant response between surface and probe is maintained. The atomicforce microscope (AFM) belongs to the group of SPM's that sense theatomic forces between the probe and surface. The technique givesfeatures of few nanometers, however the technique suffers from

-   1. Topographical distortions of image due to folding of probe shape    and surface.-   2. Structures having high aspect ratio cannot be measured.

Both the electron beam imaging and the scanning probe microscopy sufferfrom being operator demanding and time consuming. Another limitation tothese techniques is lack of measuring embedded structures in samples.

Optical profilometry is a method where a light beam having a small spotsize is applied to produce an image of the surface of a sample.Interference between light reflected from the sample and a known surfaceis used to obtain height information. Thus, scanning across the surfaceprovides the topographic image of the sample. The method has potentialof conducting vertical measurements very accurately. However, resolutionof lateral features is limited by the spot size of the light beam, whichis in the range of a micron.

In contrast, the herein presented method and apparatus of the inventionprovide with an improved characterization technique to obtain spatialfeatures of symmetric and asymmetric semi-periodic structure located atthe surface or embedded in nearly planar samples. The apparatus collectssufficient data for uniquely determination of the arbitrary shapedprofile. The measurement of the semi-repeated structure isnon-destructive, fast, accurate, reproducible and reliable.

U.S. Pat. No. 5,963,329 discloses an apparatus and a method fordetermining the profile of periodic lines on a substrate. The substrateis illuminated with a broadband light and light diffracted by thestructure is collected, measured and recorded as function of wavelength.The determination of the profile is conducted as follows. The intensityof the diffracted light is calculated from a seed model of the profileusing Maxwell's equations. Comparison between the calculated intensityand the collected intensity vs. wavelength curve is performed to adjustthe parameters of the model such that the measured and modeledintensities eventually match.

However, the apparatus and method of U.S. Pat. No. 5,963,329 has thefollowing disadvantages:

-   1. It may only be applied to symmetric periodic line structures,-   2. the recorded data used in the profile determination is only    sufficient for symmetric structures. An attempt to extend the    described invention to asymmetric profiles will lead to    un-determined equation systems that are incapable of calculating the    profile in a unique way, and-   3. it may only be applied to repeated structures having collinear    grating vectors.

U.S. Pat. No. 6,281,974 discloses a method for measuring at least onedesired parameter of a patterned structure having a plurality offeatures defined by a certain process of its manufacturing. Thestructure represents a grid having at least one cycle formed of at leasttwo locally adjacent elements having different optical properties inrespect of an Incident radiation. An optical model, based on at leastsome of the features of the structure is provided. The model is capableof determining theoretical data representative of photometricintensities of light components of different wavelengths specularlyreflected from the structure and of calculating said at least onedesired parameter of the structure. A measurement area, which issubstantially larger than a surface area of the structure defined by thegrid cycle, is illuminated by an incident radiation of a presetsubstantially wide wavelength range. Light component substantiallyspecularly reflected from the measurement area is detected and measureddata representative of photometric intensities of each wavelength withinthe wavelength range is obtained. The measured and theoretical datasatisfies a predetermined condition. Upon detecting that thepredetermined condition is satisfied, said at least one parameter of thestructure is calculated.

The method disclosed in U.S. Pat. No. 6,281,974 suffers from basicallythe same drawbacks as U.S. Pat. No. 5,963,329—namely, that since onlyinformation in the zero order diffraction beam is recorded the profiledetermination is only sufficient for symmetric structures. An attempt toapply the method of U.S. Pat. No. 6,281,974 to asymmetric profiles willlead to un-determined equation systems that are incapable of calculatingthe profile in an unambiguous manner.

In view of the problems and disadvantages discussed above there is aneed for an improved technique for quality control of microstructuresthat reduces the profile measurements uncertainties and avoids damagingof the microstructure to be tested. Furthermore, the requirements forhigh quality profile measurements are relaxed with the presentinvention, thus decreasing the complexity and cost for quality controlInspection of microstructures.

Thus, it is an object of the present invention to provide anon-destructive optical method and an apparatus for rapid, accurate,reproducible, unique and reliable determination of the surfacetopography of samples having semi-periodic structures deposited directlyonto a nearly planar sample, or onto a film deposited on a nearly planarsample, or embedded within a film.

It is a further object of the present invention to provide a method fordetermination of the 3D profile of the semi-periodic structure based onmeasurements of light diffracted from the sample having thesemi-periodic structure.

SUMMARY OF THE INVENTION

It is well known that diffracted light generated by illumination ofperiodic structures are strongly dependent on the geometry and materialproperties of the structure. The present invention utilizes thegeometrical sensitivity of diffraction to determine the profile shape ofthe periodic structure. More specific, the present invention relates toa method and an apparatus for measuring the profile shape of asemi-periodic structure. By a semi-periodic structure means a samplehaving locally two-dimensional array of almost identicalthree-dimensional elements on a planar surface, a sample having locallytwo-dimensional array of almost identical three-dimensional elements ona film, or embedded within a film.

A collimated light beam diffracted by a periodic structure generates adiscrete set of propagating beams. The directions of these diffractedbeams are solely given by the local periodicity of the repeatedstructure. The intensity distribution of the diffracted beams, however,depends strongly of the profile shape of the repeated structure. Thisdependency on the incident illumination angle, wavelengths, anddiffraction order are used to reconstruct the arbitrary shaped profileof the repeating structure. A direct implication of the dependency isfor instance used to distinguish between symmetric and asymmetricmicrostructures in the following way. The diffraction intensitynormalized to the incident light, for a symmetric profile produces evenand odd diffraction orders of equal magnitude, whereas the diffractionintensity normalized to the incident light, for an asymmetric profilegenerally produces even and odd diffraction orders of non-equalmagnitude.

The above-mentioned objects are complied with by providing, in a firstaspect, an apparatus for measuring geometrical profiles of periodicmicrostructures of a sample, the apparatus comprising

-   -   a light source for emission of a light beam,    -   polarizing means for polarizing the emitted light beam,    -   focusing means for focusing the polarized light beam on the        microstructures of the sample so as to provide, at a number of        microstructures, a plurality of illumination angles        simultaneously,    -   a collection means for collecting light diffracted from the        illuminated microstructures,    -   resolving means for resolving the collected light into        diffraction data relating to illumination angles, polarization        angles, diffraction orders, and illumination wavelengths, and    -   a reconstruction algorithm for determining the geometrical        profile of the Illuminated microstructures, the reconstruction        algorithm being adapted to perform the following steps:        -   comparing the resolved diffraction data with modeled            diffraction data from a known geometrical profile, the known            geometrical profile being selected from a database of            pre-defined families of profiles,        -   or        -   comparing the resolved diffraction data with modeled            diffraction data from a known parameterized geometrical            profile, the known parameterized geometrical profile being            selected by variation of the geometrical profile parameters,            the selection of the parameters being performed using            minimum norm techniques,        -   the selection being performed using minimum norm techniques,        -   repeating adjusting the geometrical profile of the known            selected geometrical profile until the modeled diffraction            data matches the resolved diffraction data within            predetermined tolerances.

The light source may comprise a broadband light source, such as Xenon,Deuterium, or halogen lamp. Alternatively, the light source may comprisea substantially monochromatic light source, such as a laser. Thefocusing means and the collection means may comprise a lens system. Thefocusing means and the collection means may each comprise a lens system,which could be the same lens system.

The polarizing means may comprise a beam splitter, the beam splittergenerating a reference beam and an illumination beam. The resolvingmeans may comprise an Imaging detection system.

The imaging detection system may comprise means for generating aplurality of light beams having different center wavelengths andpropagating in different directions. The imaging detection system mayfurther comprise an array of light sensitive elements, the array oflight sensitive elements being adapted to be illuminated by thegenerated plurality of light beams.

Alternatively, the imaging detection system may comprise an array ofcolor light sensitive elements, the color sensitivity being provided bya color mask positioned in front of the light sensitive elements. Thearray of light sensitive elements may form part of a CCD array, anInGaAs array, a PbSe array, a PbS array, a superconduction TunnelJunction array, or any combination thereof.

In a second aspect, the present invention relates to a non-destructivemethod for measuring geometrical profiles of periodic microstructures ofa sample, the method comprising the steps of:

-   -   providing a light source for emission of a light beam,    -   polarizing the emitted light beam, and transmitting the        polarized light beam to a refractive member,    -   focusing the transmitted and polarized light beam on the        microstructures of the sample using the refractive member so as        to provide, at a number of microstructures, a plurality of        illumination angles simultaneously,    -   collecting light diffracted from the illuminated microstructures        using a collection system, and resolving the collected light        into diffraction data relating to illumination angles,        polarization angles, diffraction orders, and illumination        wavelengths, and    -   determining the geometrical profile of the illuminated        microstructures using a reconstruction algorithm, the        reconstruction algorithm comprising the steps of:        -   comparing the resolved diffraction data with modeled            diffraction data from a known geometrical profile, the known            geometrical profile being selected from a database of            pre-defined families of profiles,        -   or        -   comparing the resolved diffraction data with modeled            diffraction data from a known parameterized geometrical            profile, the known parameterized geometrical profile being            selected by variation of the geometrical profile parameters,            the selection of the parameters being performed using            minimum norm techniques,        -   the selection being performed using minimum norm techniques,        -   repeating adjusting the geometrical profile of the known            selected geometrical profile until the modeled diffraction            data matches the resolved diffraction data within            predetermined tolerances.

In a third aspect, the present invention relates to the use of themethod according to the second aspect for monitoring formation oralternation of periodic microstructures.

The formation or alternation may be monitored by monitoring respectiveformation or alternation of the microstructures. Alternatively, theformation or alternation may be monitored by monitoring formation oralternation of an associated target structure.

The periodic microstructures may be formed or altered in asemiconductor, metallic, or dielectric material, or combination thereof.The periodic microstructures may be formed or altered using an etchingmethod, such as reactive plasma etching and wet etching. The periodicmicrostructures may also be formed using lithographic processes,epitaxial growth processes, film deposition processes, or oxidationprocesses or any combination hereof.

In a fourth aspect, the present invention relates to a computer programcode for determining a geometrical profile of illuminatedmicrostructures when said program code is run on a computer, the programcode being adapted to perform the following steps:

-   -   resolving collected light data into diffraction data relating to        illumination angles, polarization angles, diffraction orders,        and illumination wavelengths,    -   comparing the resolved diffraction data with modeled diffraction        data from a known geometrical profile, the known geometrical        profile being selected from a database of pre-defined families        of profiles,    -   or    -   comparing the resolved diffraction data with modeled diffraction        data from a known parameterized geometrical profile, the known        parameterized geometrical profile being selected by variation of        the geometrical profile parameters, the selection of the        parameters being performed using minimum norm techniques,    -   the selection being performed using minimum norm techniques, and    -   repeating adjusting the geometrical profile of the known        selected geometrical profile until the modeled diffraction data        matches the resolved diffraction data within predetermined        tolerances.

In a fifth aspect, the present invention relates to a computer readablemedium carrying a computer program code for determining a geometricalprofile of illuminated microstructures when said program code is run ona computer, the program code being adapted to perform the followingsteps:

-   -   resolving collected light data into diffraction data relating to        illumination angles, polarization angles, diffraction orders,        and illumination wavelengths,    -   comparing the resolved diffraction data with modeled diffraction        data from a known geometrical profile, the known geometrical        profile being selected from a database of pre-defined families        of profiles,    -   or    -   comparing the resolved diffraction data with modeled diffraction        data from a known parameterized geometrical profile, the known        parameterized geometrical profile being selected by variation of        the geometrical profile parameters, the selection of the        parameters being performed using minimum norm techniques,    -   the selection being performed using minimum norm techniques, and    -   repeating adjusting the geometrical profile of the known        selected geometrical profile until the modeled diffraction data        matches the resolved diffraction data within predetermined        tolerances.

In one embodiment, the invention is directed to a method for obtainingthe profile shape from a semi-periodic symmetric microstructure. Themethod includes adjustment of working distance between microstructureand collimating optics, selection of wavelength range, selection ofillumination angle, selection of diffraction order, selection ofpolarization angle to be measured, set the convergence limits, selectionof a seed model for the computer calculations and detection of thereflected diffracted intensity normalized to the intensity of theincident light for the selected wavelengths or the detected lightintensity of a known and qualified reference sample without a repeatedstructure for the selected wavelengths. The recorded data is processedby the apparatus using an algorithm for determining the profile shape ofthe microstructure by adjusting the topography of the seed profile untilthe calculated diffraction intensities match the measured diffractionintensities within the specified success criteria.

In another embodiment, the invention is directed to a method forobtaining the profile shape from a semi-periodic symmetricmicrostructure. The method includes adjustment of working distancebetween microstructure and collimating optics, selection of wavelengthrange, selection of illumination angle, selection of diffraction order,selection of polarization angle to be measured, set the convergencelimits, and detection of the reflected diffracted intensity normalizedto the intensity of the incident light for the selected wavelengths orthe detected light intensity of a known and qualified reference samplewithout a repeated structure for the selected wavelengths. The recordeddata is processed by the apparatus using an algorithm for determiningthe profile shape of the microstructure by adjusting the topography ofthe profile found from the measured diffraction intensities until thecalculated diffraction intensities match the measured diffractionintensities within the specified success criteria.

In another embodiment, the invention is directed to a method forobtaining the profile shape from a semi-periodic symmetricmicrostructure. The method includes adjustment of working distancebetween microstructure and collimating optics, selection of wavelength,selection of illumination angle range, selection of diffraction order,selection of polarization angle to be measured, set the convergencelimits, selection of a seed model for the computer calculations anddetection of the reflected diffracted intensity normalized to theintensity of the incident light for the selected illumination angles orthe detected light intensity of a known and qualified reference samplewithout a repeated structure for the selected illumination angles. Therecorded data is processed by the apparatus using an algorithm fordetermining the profile shape of the microstructure by adjusting thetopography of the seed profile until the calculated diffractionintensities match the measured diffraction intensities within thespecified success criteria.

In another embodiment, the invention is directed to a method forobtaining the profile shape from a semi-periodic symmetricmicrostructure. The method includes adjustment of working distancebetween microstructure and collimating optics, selection of wavelength,selection of illumination angle range, selection of diffraction order,selection of polarization angle to be measured, set the convergencelimits, and detection of the reflected diffracted intensity normalizedto the intensity of the incident light for the selected illuminationangles or the detected light intensity of a known and qualifiedreference sample without a repeated structure for the selectedillumination angles. The recorded data is processed by the apparatususing an algorithm for determining the profile shape of themicrostructure by adjusting the topography of the profile found from themeasured diffraction intensities until the calculated diffractionintensities matches the measured diffraction intensities within thespecified success criteria.

Guided by the descriptive pattern of the four embodiments the remainingembodiments are listed in TABLE 1 for clarity and legibility. Thealready described embodiments are also included in the table.

BRIEF DESCRIPTION OF THE DRAWINGS

The above set forth and other features of the invention will be moreapparent when read in connection with the accompanying drawings,wherein:

FIG. 1 defines the propagation of light incident on a sample having arepeated structure. The propagation direction is given by the polarangle θ and the azimuth angle φ. The polarization of the light isspecified by the angle Φ with respect to the unit vectors e_(s) ande_(p). These vectors represent the TE mode and the TM mode,respectively. The vector e_(s) is in the plane of incidence and e_(p) isperpendicular to it, and both being orthogonal to the incident wavevector k. The Cartesian coordinate system has the x-axis along one ofthe periodic directions.

FIG. 2 is a three-dimensional periodic sample, and more specifically, atwo-dimensional array of symmetric and rectangular elements on asurface. The parameters for the periodic structure are included.

FIG. 3 is an three-dimensional periodic sample, and more specifically, atwo-dimensional array of elements that is slightly altered from therectangular shape of FIG. 2 to an asymmetric shape composed of multipleslabs. The parameters for the periodic structure are included.

FIG. 4 is showing calculated diffraction efficiency as function ofwavelength curves for various diffraction orders for the symmetricstructure given in FIG. 2.

FIG. 5 is showing calculated diffraction efficiency as function ofwavelength curves for various diffraction orders for the asymmetricstructure given in FIG. 3.

FIG. 6 is showing the difference between the symmetric and asymmetric ofcalculated diffraction efficiency as function of wavelength curves shownin FIG. 4 and FIG. 5 demonstrating the sensitivity of diffractionefficiencies to small changes of the repeated profile shape.

FIG. 7 is showing calculated diffraction efficiency as function ofincident illumination angle curves for various diffraction orders forthe symmetric structure given in FIG. 2.

FIG. 8 is showing calculated diffraction efficiency as function ofincident illumination angle curves for various diffraction orders forthe asymmetric structure given in FIG. 3.

FIG. 9 is showing the difference between the symmetric and asymmetric ofcalculated diffraction efficiency as function of incident illuminationangle curves shown in FIG. 7 and FIG. 8 demonstrating the sensitivity ofdiffraction efficiencies to small changes of the repeated profile shape.

FIG. 10 is illustrating the model of the repeated structure (a). Thegrating vectors a and b define the unit cell for the repeated structureand are in general non-collinear. The symbol ν denotes the angle betweenthe grating vectors. An arbitrary profile is approximated bydiscretization into multiple slabs (b) where each slab consists of M_(q)by N_(q) smaller building blocks or sub slabs (c). Building block(i,j,q) is characterized by its widths (w_(qi),w_(qj)) and off-sets(d_(qi),d_(qj)) in the lateral directions, height h_(q) and index ofrefraction n_(ijq).

FIG. 11 shows a detail of an embodiment for an optical system forcollecting reflected diffracted light intensity data sufficient todetermine the profile of the repeated structure. The focused light beamis composed of rays having a range of incident angle and exemplified inthe sketch by a ray of incident angle θ. The detection of the reflecteddiffracted ray is illustrated to have a one-to-one relation between theIncident angle and the location on the detector array (higher orders areneglected for simplicity).

FIG. 12 shows a detail of an embodiment for an optical system forcollecting reflected diffracted light intensity data sufficient todetermine the profile of the repeated structure. The collimated andpolarized light is focused by a lens system onto the periodic structureof a sample. The periodicity of the sample diffracts the light indiscreet and distinct directions. The detection of the reflecteddiffracted light is illustrated to have a one-to-one relation betweenthe diffraction order and the location on the detector array.

FIG. 13 shows two embodiments of an optical system for collectingtransmitted diffracted light intensity data sufficient to determine theprofile of the repeated structure. One embodiment provides a collimated,polarized and monochromatic light diffracted by a sample having aperiodic structure, transmitted through the sample, and collected by animaging detector, e.g. CCD-camera. The second embodiment uses collimatedand polarized broadband light that is diffracted by a sample having aperiodic structure, transmitted through the sample, and collected by animaging spectro-detector, e.g. Superconducting Tunnel Junction(STJ)-array.

FIG. 14 shows a detail of FIG. 13. The collimated and polarized light isdirected by a lens system onto the periodic structure of a sample. Theperiodicity of the sample diffracts the light in discrete and distinctdirections. The detection of the transmitted diffracted light isillustrated to have a one-to-one relation between the diffraction orderand the location on the detector array.

FIG. 15 shows a detail of FIG. 14. The collimated and polarized light isfocused by a lens system onto the periodic structure of a sample and thefocused light is composed by an ordered set of light rays covering arange of incident angles. The transmitted diffraction light isillustrated to have a one-to-one relation between the incident angle andthe location on the detector array (higher orders are neglected forsimplicity).

FIG. 16 is a flowchart of the algorithm determining the topography ofsamples having locally periodic microstructures.

While the invention is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. Itshould be understood, however, that the invention is not intended to belimited to the particular forms disclosed. Rather, the invention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

An illustration of the principle of the invention is in FIGS. 1-9. InFIG. 1 is defined the illumination geometry of a sample having a locallyrepeated structure. The structure is Illuminated by a planeelectromagnetic wave characterized by its wavelength λ, linearpolarization Φ, and the direction of propagation given by the incidentangle θ and the azimuth angle φ. The Cartesian coordinate system has thex-axis along one of the periodic directions.

The intensity of light diffracted by the structure normalized to theintensity of the incident light, denoted as the diffraction efficiency,is calculated for a symmetric profile represented by a box in FIG. 2 andan asymmetric profile described in FIG. 3. The latter profile altersjust slightly from the rectangular profile. In FIGS. 4-6 are plotted thecalculated diffraction efficiency as function of wavelength for variousdiffraction orders, and in FIG. 7-9 are plotted the calculateddiffraction efficiency as function of incident illumination angle fordifferent diffraction orders at fixed wavelength of 200 nm. The plotsdemonstrate that symmetric profiles produces even and odd diffractionorders of equal magnitude as expected for normal illumination. This is,however, not observed for the asymmetric profile where the diffractionefficiency generally differs for even and odd orders. The sensitivity ofdiffraction intensity to minor changes is clearly observed in FIG. 6 andFIG. 9 of the symmetric and asymmetric profiles given in FIGS. 2 and 3.

The apparatus in the invention employs a light source delivering a lightbeam that is collimated, polarized and focused onto a small repeatedstructure to be measured. The focused light beam is diffracted by theperiodic structure and detected by an imaging detector. Variouspotential embodiments of the apparatus are presented in FIG. 11-16including details.

FIGS. 11 and 12 show the apparatus used to collect reflective diffractedlight during illumination of a sample having repeated structures. Acollimated and polarized light beam delivered by a broadband lightsource system is divided by a non-polarizing beam splitter. The beampassed through the beam splatter is reflected by a mirror and directedincident onto a detector array and may serve as reference measurement inorder to normalizing the diffracted signals. The other beam exits thebeam splatter with direction incident on a lens system, which focus thebeam onto the periodic structure. The reflected diffraction light,leaving the periodic structure, has discrete and distinct directions andis collected by the lens system, which directs the light incident to theimaging detection array. This lens system is designed to collectdiffracted light with large diffraction angles, i.e. propagationdirection of lower diffraction orders are within the numerical apertureof the lens system. Note that the zero-order diffracted light passesthrough the beam splitter before reaching the imaging detector.

The identification of the diffraction orders of the collecteddiffraction light is unique due to a one-to-one relation between thediffraction order and the location on the detector array as illustratedin FIG. 12. This feature provides simultaneously collection of variousorders of reflected diffraction light intensities.

The repeated structure is illuminated by a focused beam meaning that thestructure is exposed to a whole range of incident and azimuth anglessimultaneously. The reflected diffraction light from the variouspropagation directions is detected by the imaging system aftercollection by the lens system. This is exemplified in FIG. 11 by a rayof incident angle θ. The iris controls the size of the incident angleinterval. The detection of the reflected diffracted ray is illustratedto have a one-to-one relation between the propagation direction (θ,φ)and the location on the detector array. This is valid for sufficientlysmall illumination spot size on the repeated structure and obtainable byadjusting the distance between the repeated structure and the lenssystem. This feature provides simultaneously angular resolution of thereflected diffraction light intensities using a passive mechanicalmethod.

FIG. 13 shows the apparatus for collecting transmitted diffraction lightduring illumination of a transparent or semi-transparent sample havingrepeated structures. A collimated and polarized light beam delivered bya broadband light source system is directed incident on an objectivelens system, which focus the beam onto the periodic structure. Thetransmitted diffraction light, leaving the periodic structure, hasdiscrete and distinct directions and collected direct by an imagingdetection array or through another objective lens system to an imagingdetection array.

The diffraction orders of the collected diffraction light are uniquelyidentified due to a one-to-one relation between the diffraction orderand the location on the detector array as illustrated in FIG. 14. Thisfeature provides simultaneously collection of various orders oftransmitted diffraction light intensities.

Similar to the reflective diffraction apparatus the repeated structureis illuminated by a focused beam. In FIG. 15 the focused beam isrepresented by a ray of incident angle θ. The transmitted diffracted rayis illustrated to have a one-to-one relation between the propagationdirection (θ,φ) and the location on the detector array. A requirementfor the validity of the relationship is a small spot size at therepeated structure, but large enough to cover several periods in bothrepeated directions.

This feature provides simultaneously angular resolution of thetransmitted diffraction light intensities using a passive mechanicalmethod. In order to normalize to transmitted diffraction light theintensity of the light source is measured prior to the measurement.

Grating Equation and Propagation Directions

The relation between the incident direction of illumination light (θ,φ)having wavelength λ, the propagation direction (θ_(mn), φ_(mn)) ofdiffracted light of order (m,n), and the grating vectors a=Λ_(a)(1,0)and b=Λ_(b)(sin ν,cos ν) of the repeated structure, see FIG. 10, isgiven by the grating equations

$\begin{matrix}{{{{\sin\;\theta_{mn}\;\cos\;\phi_{mn}} - {\sin\;\theta\;\cos\;\phi}} = {m\;\frac{\lambda}{\Lambda_{a}}}}{{{\sin\;\theta_{mn}\;\sin\;\phi_{mn}} - {\sin\;\theta\;\sin\;\phi}} = {{{- m}\;\frac{\lambda}{\Lambda_{a}}\tan\; v} + {n\;\frac{\lambda}{\Lambda_{b}}\sec\; v}}}} & (1)\end{matrix}$where the quantities Λ_(a) and Λ_(b) are the periodicity of the gratingalong the repeated directions and ν is the angle between the gratingvectors. The wavelength of the light before and after diffraction withthe periodic structure is unchanged.

The following description outlines a workable procedure for collectingthe diffraction efficiency data.

Description of the Diffraction Efficiency Measurement with the NecessaryCorrections

The diffraction efficiency, i.e. the intensity ratio between theincoming light and the diffracted light, is recorded by the apparatususing following generic procedure for the backscattered and thetransmitted diffraction efficencies:

The apparatus for measuring backscattered diffraction efficiency,sketched in FIG. 11, and transmittive diffraction efficiency, sketchedin FIG. 13, has a light source delivering the collimated beam. Let theintensity profile of the beam be given by I_(S)(x,y) where (x,y)represents local coordinates for a cross sectional plan of the beam.Following the path of the beam the light passes a beam-splitter and alens system transforming the intensity at focal point toI _(focus)(θ,φ)=ξ_(LS)ξ_(BS) I _(S)(x,y)where (x,y)=ƒ tan θ(cos φ,sin φ) that relates the propagation direction(θ,φ) of a perfect focused ray to its corresponding location (x,y) ofthe collimated beam. The parameter ƒ is the effective focal length forthe lens system and ξ_(element) is the light intensity transfer functionof the optical elements: the beam splitter (BS) and the lens system(LS). These functions are assumed to be well known.Backscattered Diffraction Efficiencies

The efficiency of backscattered orders is revealed from measurementsof 1) the sample having the periodic structure with the repeatedstructure in the focal point and 2) a plan featureless substrate ofknown material also denoted as the reference substrate placed with thesurface at the focal point. See FIG. 11.

The imaging detector signal for the reference substrate isI _(ref) ^(Detector)(x,y)=ξ′_(BS)ξ′_(LS) R(θ,φ)I _(focus)(θ,φ)  (2)where R(θ,φ) is the reflectance of a known reference substrate. Thereflectance can be found be found from Fresnel's equations and therefractive index of the reference substrate material. ξ′_(LS) andξ′_(BS) denote the intensity transfer function for light entering thelens system and beam splitter in opposite direction.

The imaging detector signal for the sample having a periodic structureis

$\begin{matrix}{{I_{sample}^{Detector}( {x_{mn},y_{mn}} )} = \{ \begin{matrix}{\xi_{BS}^{\prime}\xi_{LS}^{\prime}{\eta_{00}( {\theta,\phi} )}\;{I_{focus}( {\theta,\phi} )}} & {( {m,n} ) = ( {0,0} )} \\{\xi_{LS}^{\prime}{\eta_{mn}( {\theta_{mn},\phi_{mn}} )}\;{I_{focus}( {\theta,\phi} )}} & {else}\end{matrix} } & (3)\end{matrix}$where η_(mn) is the backscattered diffraction efficiency of order (m,n).For a perfect lens system the various diffraction orders are detected at(x_(mn), y_(mn))=ƒ tan θ_(mn)(cos φ_(mn),sin φ_(mn)) of the imagingdetector array. The relation between the propagation directions for theincident and diffracted rays, (θ,φ) and (θ_(mn),φ_(mn)), (respectively,is given by the grating equation (1).

Thus, the efficiency for backscattered diffraction orders is, after useof Eq. 2 and Eq. 3,

$\begin{matrix}{{\eta_{mn}( {\theta_{mn},\phi_{mn}} )} = \{ \begin{matrix}{R\;\frac{I_{sample}^{Detector}( {x,y} )}{I_{ref}^{Detector}( {x,y} )}} & {( {m,n} ) = ( {0,0} )} \\{\xi_{BS}^{\prime}R\;\frac{I_{sample}^{Detector}( {x_{mn},y_{mn}} )}{I_{ref}^{Detector}( {x,y} )}} & {else}\end{matrix} } & (4)\end{matrix}$Transmitted Diffraction Efficiencies

The efficiency of transmitted orders is obtained from 1) measurements ofa semi-transparent sample having the periodic structure with therepeated structure in the focal point and 2) direct measurement of thefocused light leaving the lens at the same optical distance as thesample. See FIG. 13.

The imaging detector signal for the reference light isI _(ref) ^(Detector)(x,y)=I _(focus)(θ,φ)  (5)where (x,y)=z tan θ(cos φ,sin φ) is the detection location on theimaging array for rays leaving the lens system having propagatingdirection (θ,φ). The coefficient z is the distance of the detector arrayto the focal point.

The imaging detector signal for the sample having a periodic structureisI _(sample) ^(Detector)(x,y)=η_(mn)(θ_(mn),φ_(mn))I _(focus)(θ,φ)  (6)where η_(mn) is the transmitted diffraction efficiency of order (m,n).The detection location for the diffracted orders (x_(mn),y_(mn)) forrays having propagating direction of (θ_(mn),φ_(mn)) is related through(x_(mn),y_(mn))=z tan θ_(mn) (cos φ_(mn),sin φ_(mn)).

Based on the expressions for the reference and sample signals, Eq. 5 andEq. 6, the measured efficiency for the transmitted diffraction orders isfound by

$\begin{matrix}{{\eta_{mn}( {\theta_{mn},\phi_{mn}} )} = \frac{I_{sample}^{Detector}( {x_{mn},y_{mn}} )}{I_{ref}^{Detector}( {x,y} )}} & (7)\end{matrix}$

For both the reflective (backscattered) and the transmittive modes ofthe apparatus the wavelength dependence of the diffraction efficiency isachieved either by

-   1. Use of, e.g. monochromator, filtering the broad band light source    in conjunction with an image detector, say CCD-camera-   2. Use of a broadband light source in conjunction with a    spectro-imaging detector, say a Superconducting Tunnel Junction    (STJ)-array.    Algorithm

The algorithm according to the invention is depicted in FIG. 16. Priorto the measurement the acquisition parameters for the measurement ofmicrostructure are set. These parameters include adjustment of thedistance between the collimating optics and the microstructure in orderto collect the desired number of diffraction orders, selection ofwavelength range, selection of illumination angle range to be measured,specifying the acceptable success limits for the measurement. After themeasurements a computer algorithm is applied to determine themicrostructure profile. Using the measured and normalized diffractionintensities for the detected-orders, spectral and/or angular rangetogether with the optional seed profile the algorithm calculates themicrostructure profile in the following way.

A database of seed profiles is accessed and searched for match using themeasured data. The database consist of normalized diffractionintensities for series of profiles that are calculated using rigorouscoupled wave analysis such as the Fourier modal method outlined in“Diffraction Theory of micro-relief Gratings, in H. P. Herzig (editor)Micro-optics, pp. 31-52, London: Taylor & Francis (1997)” and in “L.U:New formulation of the Fourier modal method for crossed surface-reliefgratings, J. Opt. Soc. Am. A14 (1997)”. An arbitrary profile of therepeated structure, sketched in FIG. 10, is approximated bydiscretization into multiple slabs consisting of M_(q) by N_(q) smallerbuilding blocks. The building blocks (i,j,q) are characterized by thewidths (w_(qi),w_(qj)) and off-sets (d_(qi),d_(qj)) in the lateraldirections, height h_(q) and index of refraction n_(ijq).

The slabs are defined by the grating vectors a and b and the lateralperiodicity is given by the lengths of the grating vectors: |a|=Λ_(a)and |b|=Λ_(b). In addition to the material and geometrical quantities ofthe microstructure the model calculation requires the electromagneticparameters of the incoming light represented by plane waves: wavelengthλ, linear polarization Φ, and the direction of propagation given by theincident angle θ and the azimuth angle φ. The Cartesian coordinatesystem is defined to have the x-axis along one of the periodicdirections. See FIG. 1.

The searching technique used to select the seed model in the database isrelated to find the minimum norm difference between the measureddiffraction efficiencies and the modeled efficiencies of the seed model.Herein the basic principle applying the least squares technique (squaredL₂-norm) is demonstrated.

Each seed model is parameterized such that the geometrical shape of theprofile is represented by a continuous profile function z=profile(x,y,α)with the adjusting parameters α=(α₁,α₂, . . . , α_(u)). A simple exampleof profile functions is the rectangular profile characterized by theparameters: profile height, profile widths and periodicity in therepeated directions.

The diffraction efficiency is calculated by applying the Fourier modalmethod on a model of the sample that may consist of multiple homogenouslayers and layers with repeated structures. The profiles of theserepeated structures are approximated by multiple slabs consisting ofM_(q) by N_(q) smaller building blocks as illustrated in FIG. 10.

The database used to identify the optimum seed model in reconstructionof the profile consists of modeled diffraction efficiency data arraysfor each type of profiles. Such an array represents tabulateddiffraction efficiencies for suitable numbers of pre-defined values ofwavelength λ, direction of incidence (θ,φ), diffraction orders (m,n),polarization angle, . . . , and the adjusting parameters α=(α₁,α₂, . . ., α_(u). A seed model is selected as the model having minimum Chisquared between the measured diffraction efficiency data (θ,φ,λ,m,n, . .. ,σ,η)_(t) and the modeled efficiency data,

$\begin{matrix}{{\min\limits_{{{seed}\mspace{14mu}{model}\mspace{14mu} j}\; \in \;{database}}\lbrack {\sum\limits_{i = 1}^{N}( \frac{\eta_{i} - {\eta^{{seed}\mspace{14mu}{model}}( {\Omega_{i},\alpha_{{seed}\mspace{14mu}{model}\mspace{14mu} j}} )}}{\sigma_{i}} )^{2}} \rbrack},{\Omega_{i} = ( {\theta,\phi,\lambda,m,n,\ldots}\; )_{i}}} & (8)\end{matrix}$where σ₁ is the standard deviation of η₁.

In the case of a found seed model in the database a minimization leastsquare fitting procedure is applied to adjust the seed profile untilconvergence between the calculated and measured diffraction efficienciesis reached.

The technique of reconstructing the profile based on measured efficiencydata consists of minimization of the following normalized Chi squaredexpression

$\begin{matrix}{\chi^{2} = {\frac{1}{N}{\sum\limits_{i = 1}^{N}( \frac{\eta_{i} - {\eta( {\theta_{i},\phi_{i},\lambda_{i},m_{i},n_{i},\ldots\mspace{11mu},\alpha} )}}{\sigma_{i}} )^{2}}}} & (9)\end{matrix}$with respect to the adjusting parameters α=(α₁,α₂, . . . ,α_(u)) of theprofile model having u fitting parameters. N is the number of measuredefficiency data points (θ,φ,λ,m,n,σ, . . . , η)₁ obtained for variousdirection of incidence (θ,φ), wavelengths λ, diffraction orders (m,n),polarization angles, etc.How to Find α

Let α₀ be a good initial start vector for the profile parameters α andthe diffraction efficiency η be approximated to 1^(st) order by

${\eta( {\Omega_{i},\alpha} )} \approx {{\eta( {\Omega_{i},\alpha_{0}} )} + {\frac{\partial\eta}{\partial\alpha}( {\Omega_{i},\alpha_{0}} )\;\Delta\;\alpha}}$where Δα=α−α₀ and Ω=(θ,φ,λ,m,n, . . . ). Thus, the Chi Squaredexpression in Eq. (9) can be approximated by

$\begin{matrix}\begin{matrix}{\chi^{2} \approx {\frac{1}{N}\;{\sum\limits_{i = 1}^{N}( \frac{\eta_{i} - \{ {{\eta( {\Omega_{i},\alpha_{0}} )} + {\frac{\partial\eta}{\partial\alpha}( {\Omega_{i},\alpha_{0}} )\;\Delta\;\alpha}} \}}{\sigma_{i}} )^{2}}}} \\{\mspace{31mu}{= {\frac{1}{N}( {\eta^{measured} - \eta_{0} - {\frac{\partial\eta_{0}}{\partial\alpha}\Delta\;\alpha}} )^{2}}}} \\{where} \\{{\eta^{measured} = ( {\frac{\eta_{1}}{\sigma_{1}},\frac{\eta_{2}}{\sigma_{2}},\ldots\mspace{11mu},\frac{\eta_{N}}{\sigma_{N}}} )},} \\{\eta_{0} = {( {\frac{\eta( {\Omega_{1},\alpha_{0}} )}{\sigma_{1}},\frac{\eta( {\Omega_{2},\alpha_{0}} )}{\sigma_{2}},\ldots\mspace{11mu},\frac{\eta( {\Omega_{N},\alpha_{0}} )}{\sigma_{N}}} )\mspace{14mu}{and}}} \\{\frac{\partial\eta_{0}}{\partial\alpha} = {\lbrack \frac{\partial{\eta( {\Omega_{1},\alpha_{0}} )}}{\partial\alpha} \middle| \frac{\partial{\eta( {\Omega_{2},\alpha_{0}} )}}{\partial\alpha} \middle| \ldots \middle| \frac{\partial{\eta( {\Omega_{N},\alpha_{0}} )}}{\partial\alpha} \rbrack.}}\end{matrix} & (10)\end{matrix}$

Eq. 10 is well-known from linear algebra and is formally minimized for

$\begin{matrix}{{\frac{\partial\eta_{0}^{T}}{\partial\alpha}\;\frac{\partial\eta_{0}}{\partial\alpha}\Delta\;\alpha} = {\frac{\partial\eta_{0}^{T}}{\partial\alpha}\;( {\eta^{measured} - \eta_{0}} )}} & (11)\end{matrix}$and leads to a new estimate of α=α₀+Δα. By repeated use of Eq. 11 theparameters α for the profile of the measured sample are returned.

If the calculated data is within the specified success criteria we arefinished and the calculated profile is shown and saved to a mediatogether with the diffraction efficiencies. A potential successcriterion may be Chi Squared values of Eq. (10) within the statisticalconfidence limits as expected for the χ²-distribution for N independentpoints.

For speeding up the process of determining the parameter α an array ofcalculated diffraction efficiencies η are generated or-retrieved from atable in order to approximate the efficiency η and its derivatives

$\frac{\partial\eta}{\partial\alpha}$rapidly. The array consists of efficiency values tabulated for θ=θ₀+δθj,φ=φ₀+δφk, . . . , α₁=α₁₀+δα_(i)l, where j,k, . . . , l are integers,i=1, . . . , u, and δθ, δφ, . . . , δα₁ are carefully selected steplengths.

Any value of the diffraction efficiency within the domain of the arraycan be interpolated to e.g. following second order approximation in Δαaround α₀,η_(app)(Ω,α)≈C+bΔα+Δα ^(T) AΔαusing neighboring values centered around α₀ to determine thecoefficients C, b and A. For known coefficients C, b and A thederivative

$\frac{\partial\eta}{\partial\alpha}$is easily obtained.

Chi Squared comparison between the measured efficiency data and thecalculated efficiency in the array is used to select the initial guessof the profile parameters α.

A Method of Process Control

The manufacturing of microstructures in the semiconductor and thetelecommunication industries include processes of etching, filmdeposition, oxidation, lithographic techniques, and epitaxial techniquesusually conducted in special environmental conditions.

Many of the processes are run from a recipe (pressure, duration,temperature etc.) and testing of the produced structures is undertakenafter finalized processing. A consequence of the lack of control duringthe manufacturing process itself is an increased rejection level ofmicrostructures resulting in a reduced yield.

A method of improving the process is applying in-situ or nearlyreal-time monitoring of the structures during the manufacturing processand thereby provide with continuously information on the actual featuresbeing developed and their dimensions such as depth, line width etc. Thisinformation can be used to adjust the process parameters, or as stopcriterion, or for termination of the process if the specified tolerancesare outside range.

The performance of pattern transfer process techniques such aslithography and reactive plasma etching is frequently challenged inorder to make telecommunication and semiconductor microstructures wherefeature sizes, e.g. depth, sidewall slope and line width, are critical.

Processes used to produce layers or films include deposition,sputtering, evaporation, epitaxial growth and oxidation techniques arecritical in the semiconductor and telecommunication industries wherepatterned structures are covered by a film. The critical issues aremultifarious: 1) good step coverage of structures with steep sidewall inorder to form a barrier to prevent diffusion of e.g. metal 2)planarization of deposited dielectrica is critical for structures havingpatterned conductors and dielectric in multiple layers. Lack ofplanarization induces interconnect problems.

The examples given above of formation of structures using the previouslymentioned process techniques illustrate some of the process controlapplications of the invention described herein.

The concept of the method according to the present invention is todirect a light beam towards a single target or multiple targets on thesubstrate where a semi-periodic structure is being formed or alreadypresent through a process window, optical fiber or other means foraccess of the beam to the target(s). The transmitted or thebackscattered diffracted light are continuously analyzed to providenearly real time information about the trench depth, profile width, orany other geometrical parameter that might be valuable or critical. Thecollection of the diffracted light may be obtained using the sameprocess and other windows, optical fibers or other means for thediffracted light to reach the detector of the invention.

It is important to stress that the structure being manufactured does notnecessarily itself need to contain a periodic structure in order toperform the process control. Instead the substrate can have target areasoutside the mother structure areas where periodic structures can beformed or already exist. These process control target areas containperiodic structures that have feature sizes, such as pitch, line width,notch size and depth, characteristic for the mother structure.

The developed structure can, by applying the method according to thepresent invention, be monitored for critical feature sizes in nearlyreal time and in-situ. This also includes uniformity control bymeasuring at multiple locations simultaneously or scanning.

TABLE 1 Wavelength Polarization Propagation Diffraction Seed MeasurementEmbodiment λ Φ direction (θ, φ) order (m, n) Profile model mode 1 RangeFixed Fixed Fixed Symmetric Yes Transmitive 2 Range Fixed Fixed FixedSymmetric No Transmitive 3 Fixed Fixed Range Fixed Symmetric YesTransmitive 4 Fixed Fixed Range Fixed Symmetric No Transmitive 5 RangeFixed Fixed Multiple Symmetric Yes Transmitive 6 Range Fixed FixedMultiple Symmetric No Transmitive 7 Fixed Fixed Range Multiple SymmetricYes Transmitive 8 Fixed Fixed Range Multiple Symmetric No Transmitive 9Range Fixed Fixed Multiple Asymmetric Yes Transmitive 10 Range FixedFixed Multiple Asymmetric No Transmitive 11 Fixed Fixed Range MultipleAsymmetric Yes Transmitive 12 Fixed Fixed Range Multiple Asymmetric NoTransmitive 13 Range Fixed Range Multiple Symmetric Yes Transmitive 14Range Fixed Range Multiple Symmetric No Transmitive 15 Range Fixed RangeMultiple Asymmetric Yes Transmitive 16 Range Fixed Range MultipleAsymmetric No Transmitive 17 Range Fixed Fixed Fixed Symmetric YesReflective 18 Range Fixed Fixed Fixed Symmetric No Reflective 19 FixedFixed Range Fixed Symmetric Yes Reflective 20 Fixed Fixed Range FixedSymmetric No Reflective 21 Range Fixed Fixed Multiple Symmetric YesReflective 22 Range Fixed Fixed Multiple Symmetric No Reflective 23Fixed Fixed Range Multiple Symmetric Yes Reflective 24 Fixed Fixed RangeMultiple Symmetric No Reflective 25 Range Fixed Fixed MultipleAsymmetric Yes Reflective 26 Range Fixed Fixed Multiple Asymmetric NoReflective 27 Fixed Fixed Range Multiple Asymmetric Yes Reflective 28Fixed Fixed Range Multiple Asymmetric No Reflective 29 Range Fixed RangeMultiple Symmetric Yes Reflective 30 Range Fixed Range MultipleSymmetric No Reflective 31 Range Fixed Range Multiple Asymmetric YesReflective 32 Range Fixed Range Multiple Asymmetric No Reflective

1. An apparatus for measuring geometrical profiles of periodicmicrostructures of a sample, the apparatus comprising a light source foremission of a light beam, polarizing means for polarizing the emittedlight beam, focusing means for focusing the polarized light beam on themicrostructures of the sample so as to provide, at a number ofmicrostructures, a plurality of illumination angles simultaneously, acollection means for collecting light diffracted from the illuminatedmicrostructures, the collection means being adapted to collect both the0'th and higher diffraction orders, resolving means for resolving thecollected light into diffraction data relating to illumination angles,polarization angles, diffraction orders, and illumination wavelengths,and a reconstruction algorithm for determining the geometrical profileof the illuminated microstructures, the reconstruction algorithm beingadapted to perform the following steps: comparing the resolveddiffraction data with modeled diffraction data from a known geometricalprofile, the comparison taking both the 0'th and higher diffractionorders into account, the known geometrical profile being selected from adatabase of pre-defined families of profiles, the selection beingperformed using minimum norm techniques, repeating adjusting thegeometrical profile of the known selected geometrical profile until themodeled diffraction data matches the resolved diffraction data withinpredetermined tolerances.
 2. An apparatus according to claim 1, whereinthe light source comprises a broadband light source, such as Xenon,Deuterium, or halogen lamp.
 3. An apparatus according to claim 1,wherein the focusing means comprises a lens system.
 4. An apparatusaccording to claim 1, wherein the light source comprises a substantiallymonochromatic light source, such as a laser.
 5. An apparatus accordingto claim 1, wherein the collection means comprises a lens system.
 6. Anapparatus according to claim 1, wherein the focusing means and thecollection means each comprises a lens system.
 7. An apparatus accordingto claim 6, wherein the lens systems of the focusing means and thecollection means are the same lens system.
 8. An apparatus according toclaim 1, wherein the polarizing means comprises a beam splitter, thebeam splitter generating a reference beam and an illumination beam. 9.An apparatus according to claim 1, wherein the resolving means comprisesan imaging detection system.
 10. An apparatus according to claim 9,wherein the imaging detection system comprises means for generating aplurality of light beams having different center wavelengths andpropagating in different directions.
 11. An apparatus according to claim10, wherein the imaging detection system further comprises an array oflight sensitive elements, the array of light sensitive elements beingadapted to be illuminated by the generated plurality of light beams. 12.An apparatus according to claim 11, wherein the array of light sensitiveelements forms part of a CCD array, an InGaAs array, a PbSe array, a PbSarray, a Superconduction Tunnel Junction array, or any combinationthereof.
 13. An apparatus according to claim 9, wherein the imagingdetection system comprises an array of color light sensitive elements,the color sensitivity being provided by a color mask positioned in frontof the light sensitive elements.
 14. An apparatus according to claim 13,wherein the array of light sensitive elements forms part of a CCD array,an InGaAs array, a PbSe array, a PbS array, a Superconduction TunnelJunction array, or any combination thereof.
 15. A non-destructive methodfor measunng geometrical profiles of periodic microstructures of asample, the method comprising the steps of: providing a light source foremission of a light beam, polarizing the emitted light beam, andtransmitting the polarized light beam to a refractive member, focusingthe transmitted and polarized light beam on the microstructures of thesample using the refractive member so as to provide, at a number ofmicrostructures, a plurality of illumination angles simultaneously,collecting light diffracted from the illuminated microstructures using acollection system, the collection system being adapted to collect boththe 0'th and higher diffraction orders, and resolving the collectedlight into diffraction data relating to illumination angles,polarization angles, diffraction orders, and illumination wavelengths,and determining the geometrical profile of the illuminatedmicrostructures using a reconstruction algorithm, the reconstructionalgorithm comprising the steps of: comparing the resolved diffractiondata with modeled diffraction data from a known geometrical profile, thecomparison taking both the 0'th and higher diffraction orders intoaccount, the known geometrical profile being selected from a database ofpre-defined families of profiles, the selection being performed usingminimum norm techniques, repeating adjusting the geometrical profile ofthe known selected geometrical profile until the modeled diffractiondata matches the resolved diffraction data within predeterminedtolerances.
 16. Use of the method according to claim 15 for monitoringformation or alternation of periodic microstructures.
 17. The use of themethod according to claim 16, wherein the formation or alternation ismonitored by monitoring respective formation or alternation of themicrostructures.
 18. The use of the method according to claim 16,wherein the formation or alternation is monitored by monitoringformation or alternation of an associated target structure.
 19. The useof the method according to claim 16, wherein the periodicmicrostructures are formed or altered in a semiconductor, metallic, ordielectric material, or combination thereof.
 20. The use of the methodaccording to claim 19, wherein the periodic microstructures are formedor altered using an etching method, such as reactive plasma etching andwet etching.
 21. The use of the method according to claim 19, whereinthe periodic microstructures are formed using a lithographic process.22. The use of the method according to claim 19, wherein the periodicmicrostructures are formed or altered using an epitaxial growth process.23. The use of the method according to claim 19, wherein the periodicmicrostructures are formed or altered using a film deposition process.24. The use of the method according to claim 19, wherein the periodicmicrostructures are formed or altered using an oxidation process.
 25. Anapparatus for measuring geometrical profiles of periodic microstructuresof a sample, the apparatus comprising a light source for emission of alight beam, polarizing means for polarizing the emitted light beam,focusing means for focusing the polarized light beam on themicrostructures of the sample so as to provide, at a number ofmicrostructures, a plurality of illumination angles simultaneously, acollection means for collecting light diffracted from the illuminatedmicrostructures, the collection means being adapted to collect both the0'th and higher diffraction orders, resolving means for resolving thecollected light into diffraction data relating to illumination angles,polarization angles, diffraction orders, and illumination wavelengths,and a reconstruction algorithm for determining the geometrical profileof the illuminated microstructures, the reconstruction algorithm beingadapted to perform the following steps: comparing the resolveddiffraction data with modeled diffraction data from a knownparameterized geometrical profile, the comparison taking both the 0'thand higher diffraction orders into account, the known parameterizedgeometrical profile being selected by variation of the geometricalprofile parameters, the selection of the parameters being performedusing minimum norm techniques, repeating adjusting the geometricalprofile of the known selected geometrical profile until the modeleddiffraction data matches the resolved diffraction data withinpredetermined tolerances.
 26. An apparatus according to claim 25,wherein the light source comprises a broadband light source, such asXenon, Deuterium, or halogen lamp.
 27. An apparatus according to claim25, wherein the focusing means comprises a lens system.
 28. An apparatusaccording to claim 25, wherein the light source comprises asubstantially monochromatic light source, such as a laser.
 29. Anapparatus according to claim 25, wherein the collection means comprisesa lens system.
 30. An apparatus according to claim 25, wherein thefocusing means and the collection means each comprises a lens system.31. An apparatus according to claim 30, wherein the lens systems of thefocusing means and the collection means are the same lens system.
 32. Anapparatus according to claim 25, wherein the polarizing means comprisesa beam splitter, the beam splitter generating a reference beam and anillumination beam.
 33. An apparatus according to claim 25, wherein theresolving means comprises an imaging detection system.
 34. An apparatusaccording to claim 33, wherein the imaging detection system comprisesmeans for generating a plurality of light beams having different centerwavelengths and propagating in different directions.
 35. An apparatusaccording to claim 34, wherein the imaging detection system furthercomprises an array of light sensitive elements, the array of lightsensitive elements being adapted to be illuminated by the generatedplurality of light beams.
 36. An apparatus according to claim 35,wherein the array of light sensitive elements forms part of a COD array,an InGaAs array, a PbSe array, a PbS array, a Superconduction TunnelJunction array, or any combination thereof.
 37. An apparatus accordingto claim 34, wherein the imaging detection system comprises an array ofcolor light sensitive elements, the color sensitivity being provided bya color mask positioned in front of the light sensitive elements.
 38. Anapparatus according to claim 37, wherein the array of light sensitiveelements forms part of a CCD array, an InGaAs array, a PbSe array, a PbSarray, a Superconduction Tunnel Junction array, or any combinationthereof.
 39. A non-destructive method for measuring geometrical profilesof periodic microstructures of a sample, the method comprising the stepsof: providing a light source for emission of a light beam, polarizingthe emitted light beam, and transmitting the polarized light beam to arefractive member, focusing the transmitted and polarized light beam onthe microstructures of the sample using the refractive member so as toprovide, at a number of microstructures, a plurality of illuminationangles simultaneously, collecting light diffracted from the illuminatedmicrostructures using a collection system, the collection system beingadapted to collect both the 0'th and higher diffraction orders, andresolving the collected light into diffraction data relating toillumination angles, polarization angles, diffraction orders, andillumination wavelengths, and determining the geometrical profile of theilluminated microstructures using a reconstruction algorithm, thereconstruction algorithm comprising the steps of: comparing the resolveddiffraction data with modeled diffraction data from a knownparameterized geometrical profile, the comparison taking both the 0'thand higher diffraction orders into account, the known parameterizedgeometrical profile being selected by variation of the geometricalprofile parameters, the selection of the parameters being performedusing minimum norm techniques, repeating adjusting the geometricalprofile of the known selected geometrical profile until the modeleddiffraction data matches the resolved diffraction data withinpredetermined tolerances.
 40. Use of the method according to claim 39for monitoring formation or alternation of periodic microstructures. 41.The use of the method according to claim 40, wherein the formation oralternation is monitored by monitoring respective formation oralternation of the microstructures.
 42. The use of the method accordingto claim 40, wherein the formation or alternation is monitored bymonitoring formation or alternation of an associated target structure.43. The use of the method according to claim 40, wherein the periodicmicrostructures are formed or altered in a semiconductor, metallic, ordielectric material, or combination thereof.
 44. The use of the methodaccording to claim 43, wherein the periodic microstructures are formedor altered using an etching method, such as reactive plasma etching andwet etching.
 45. The use of the method according to claim 43, whereinthe periodic microstructures are formed using a lithographic process.46. The use of the method according to claim 43, wherein the periodicmicrostructures are formed or altered using an epitaxial growth process.47. The use of the method according to claim 43, wherein the periodicmicrostructures are formed or altered using a film deposition process.48. The use of the method according to claim 43, wherein the periodicmicrostructures are formed or altered using an oxidation process.